The present invention relates to a detecting method and inspection equipment. The present invention, in particular, relates a technique for detecting fine particles and defects present on a thin film substrate, a semiconductor substrate, a photomask and so on. The present invention also concerns a technique suitable for calculating the diameter of a fine particle or defect on a semiconductor wafer substrate or increasing the detection accuracy of a coordinate position of the particle or defect on the surface of an object to be inspected.
In a production line for a semiconductor substrate, a thin film substrate or the like; for the purpose of monitoring the generated dust condition of a manufacturing apparatus, foreign matter or particles deposited on the surface of the semiconductor substrate, the thin film substrate or the like are inspected. For example, with regard to the semiconductor substrate prior to a circuit pattern formation step, it is required to detect tine particles having such fine diameters of several tens of nm or smaller on the substrate. One of prior art techniques for detecting fine defects on the surface of such an inspecting object as a semiconductor substrate is disclosed, for example, in U.S. Pat. No. 5,798,829 (Patent Document 1). In the patent, the surface of a semiconductor substrate is fixedly illuminated with a condensed laser beam (, at which time the illustrated region formed on the surface of the semiconductor substrate by the laser beam will be referred to as the illustrated spot.), scattered light from particles or defects deposited on the semiconductor substrate is detected, and such particles or defects on the entire surface of the semiconductor substrate are inspected through rotation and translational motion of the semiconductor substrate. An ellipsoidal mirror is used for detecting the scattered light, a detection position on the semiconductor substrate is set at a position corresponding to a first focus of the ellipsoid of the mirror, and the light receiving surface of a light receiving element is located at a position corresponding to a second focus of the ellipsoid, so that the scattered light from a particle can be condensed with a wide solid angle and therefore even a fine particle can be detected.
In such a prior art particle/defect inspecting apparatus, in general, the detection resolution of a coordinate at a particle/defect detection position has been restricted by the dimension of the illustrated spot in a sub-scan direction of the illustrated spot. As one of recent prior arts for enabling lightening of such restriction and detection of the position coordinate of the detected particle/defect with a resolution or accuracy better than a distance between adjacent main scan locuses in the sub-scan direction, such a technique is known as disclosed in JP-A-11-295229 (Patent Document 2).
In the aforementioned prior art, from the theoretical ground that an illumination distribution at the focused point of the condensed laser beam follows a Gaussian function, the illumination distribution of illumination light within the illustrated spot on the inspection object is assumed to follow the Gaussian function (or another function similar to the Gaussian function). Thus, results of actual measured values of scattered light at a plurality of points are made to fit with the aforementioned known function, and a peak position and peak intensity of the scattered light are calculated as values seemingly closer to true values with a resolution higher than the resolution of the discrete feed of the main scan and subscan. However, the illumination distribution within the illustrated spot in an actual illumination optical system does not always follows the Gaussian function, due to the aberration of the illumination optical system or to the quality of a beam issued from a laser light source. When a difference between the actual illumination distribution of the illustrated spot and the Gaussian function is great, the peak position and peak intensity of the scattered light calculated by the aforementioned method contain a large error, as an obvious matter. Further, when a stage for moving the inspection object in such a manner as to provide rotational motion for the main scan and translational motion for the sub-scan, is used; the locus of the main scan forms not a straight line but part of a circle arc, and the curvature of the arc is smaller than the inner periphery on the inspection object, that is, sharp. As described in the prior art, when data about the scattered light and the illumination distribution of the illustrated spot are compared in a (main scan/sub-scan) coordinate system, the comparison may adversely affect the coordinate detection accuracy when no consideration is paid to the influence of the curvature. In this connection, since the particle/defect inspecting apparatus usually outputs a coordinate value for the detected particle/defect in a form expressed in a Cartesian coordinate system on the inspection object, it is desirable from the viewpoint of its principle to handle it in the Cartesian coordinate system.